Manufacture of wet-strengthened paper



Patented Sept. 17, 1940 Milton 0. Schur, Berlin, N. 11., assignor toBrown Company, Berlin, N. 11., a corporation of Maine No Drawing.Application July 19, 1937,

- Serial No. 154,465

This invention relates to the manufacture of wet-strengthened paper,that is, paper of markedly higher wet-strength than ordinarily. Whilenot restricted thereto, it deals especially with wet-strengthened paperof substantially unimpaired absorptivity and hence of particular valuefor those uses for which it is important that a paper possess anabsorptivity comparable to that of waterleaf paper and yet be ofmarkedly I higher wet-strength, than that of waterleaf paper.

While it has been found that specific sub-. stances, notably regeneratedcellulose and gelatine, can be incorporated into paper in controlledamount conducive to a wet-strengthened absorpi5 tive paper product, yeta long-continued quest for other agents capable of wet-strengtheningpaper while substantially preserving its absorptivity has shown what wasto be anticipated,

- namely, that numerous binders or sizes capable of increasing thewet-strength of paper to a significant extent are so water-repellent asto destroy-in effect the absorptivity of the paper and thatwater-soluble or water-absorbing binders, although capable of enhancingthe dry strength of the paper and preserving to a noteworthy degree theabsorptivity" of the paper, are generally of little value in improvingthe wetstrength of the paper.

I have discovered that 39 be made to function exceedingly well as a wetstrengthening agent in paper ,without detracting unduly from theabsorptivity of the paper, provided that the gum is properly alkalinizedor activated with an alkaline solution.- It is preferable to alkalinizethe gum in situ in the paper; and, to this end, an alkaline solution maybe applied to the gum-containing paper web while the web is still on thepapermaking machine, for instance, on its way to the drier, or it may beapplied to the predried, gum-containing paper web and t web redried.While aqueous solutions of various alkaline compounds, including causticsoda, caustic potash, andsimilar hydroxides, are effective and can beused as activating media for the gum, it is considered preferable at thepresent time to usesolutions of comparatively mildly alkaline compounds,such as borax and sodium carbonate, for it has been found that a paperproduct of the desired high wet-strength and other qualtities isrealized with a pH value little greater than 7 in the finished paperproduct and that it is easyto obtain such desired slight alkalinity evenwith dilute alkaline solutions of such comparatively 56 mild alkalinecompounds as have no appreciable locust bean gum can gum. While the 5Claims. ((31. 92-21) effect on the skin. Thus, when the finished paperproduct is to serve as towels, paper handkerchiefs or other skin wipes,the presence thereinv of borax or similar mildly alkaline compound inamount to impart suitable alkalinity thereto 5 has no noteworthy eifecton the skin.

The locust bean gum useful for the purposes hereof is available on themarket as a fine white powder that lends itself nicely to incorporationinto papermaking stock without any conditioning 10 treatment whateverand isx well retained by the stock. This is evidently attributable tothe fact that the powder particles swell promptly in cold water andhence become intimately attached to and/or enmeshed in the fibers of 5the papermaking stock while in aqueous suspension and while the water ofsuspension is being drained from the thin web of stock on the.papermaking machine. It thus becomes possible to add the powdered gumto the papermaking stock in the beater engine, in the head box, or atany other convenient place in the course of papermaking and thus, whileotherwise pursuing essentially a conventional papermaking practice, toproduce a paper sheet throughout which the gum is substantiallyuniformly distributed.

Because the gum can be dissolved in weakly alkaline water, it is mostsurprising that a weakly alkaline solution activates the gum so that itexerts extraordinary wet-strengthening effect on paper. The fact is,however, that mere spraying of weakly alkaline solution on the- -wet,-gum-containing web on its way to the dry end of the papermaking machineor mere clipping of the predried, gum-containing paper web in weaklyalkaline solution followed by redrying yields a finished paper productwhose wet-strength is vastly greater than that of a similar paperproduct lacking the activated 40 present invention compre- I hends theimpregnation of a paper web in dried or moist conditionwith an aqueoussolution of the gum, yet solutions of the gum are highly viscous even atvery low gum content so that they do not ordinarily lend themselves verywell to use in uniformly. impregnating the web; and

it is, moreover, more expedient from the .standpoint of a papermaker toadd the powdered gum 6 v as such to the papermaking stock, particularlyv.as the powdered gum can be quickly and uni-; V iormly dispersedthroughout the stock with ex-, cellentretention by the stock of thewater swollen gum particles throughout subsequent papermaking operationsand alkalinizing treatthat the use of excessive borax solution mightment. have the eifect of leaching out some of the gum,

For making papers of high absorbency as a simflar predried,gum-containing paper sheet. well as markedly supernormal wet-strength,as was sprayed with borax solution of 1% strength a little as 1% to oreven less of the locust in the amount of only 150%. based on the weighta bean gum, based on the dry weight of the paperof the dry gum, and thesprayed sheet redried, in making stock, may be used pursuant to thepreswhich latter case it was found that the wet-tenent invention. Ifdesired, however, the gum sile-strength of the dried product had risento may be used for the purposes hereof in amount 2.0% pounds. All of thedried, mildly alkalinized,

10 up to about 5% or in even greater amount, gum-containing paperproducts were, however, although it is usually preferable to stay withincharacterized by a wet-strength many times that I an upper limit of gumusage of about 5%, based of a paper sheet similarly made but ofwaterleaf on the dry weight of the papermaking stock, in character, thatis, containing no gum. Indeed, producing paper products of theabsorptivity the similar waterleaf paper sheet had a wet-tendesired forsuch an article as paper toweling. she-strength of only 0.20 pound. Itmight be 15 The papermaking stock used for the purposes noted that thedried, mildly alkalinized, gum-conhereof may comprise any one or amixture of varitaining paper products hereof were of substanouscellulosic fibers, such as sulphite pulp, kraft ti lly unimpa r d waterabsorbency in t s nse pulp, wood pulp refined t high alpha, cell losthat they imbibed water practically as freely and and it is to beobserved that, because of the whit'epurposes as toweling need hence hrdly .be ness of the locust bean gum, it does not: detract tres edfrom twhlteness of bl h d papermaklng In testing the paper products hereof fortheir stock into which it is incorporated, wh n a, wet-tensile-strength,the method is to moisten a 35 paper product of highest absorbency isdesired strip /2 inch Width by e s of a camel's hair and the papermakingstock is being suspended in brush pp d into Water d subjecting e s r pwater in a beater engine, the beater roll is operthus moistened orbrushed transversely at the ated in such away and for such a period oftime pl p te o e to the te si e-strength-testing 3? as to 'do littlemore than individualize the fibers or ma hi h wet-t ns -s re th re ord dy smooth out the stock sufllciently to enable the I the n'lhehlne p se st e oad n pounds which formation therefrom of a uniformly textured the ms n d ip 1' /2 inch W d h n ppo sheet on the papermaking machine. Inother at the rupture breaking p 7 words, the stock is not beaten orhydrated with a It is to he understood that the exemplary P uview towarddeveloping a paper sheet of the relaeedllles hereinbefele given e u j tto wide tively high density requirements of bond, writing, variationwithout departing from the p it or or ledger papers. On the contrary,the beater scope of t e vent on r o s efin by t engine is operatedessentially as a mixer to bring appended claims. Thus, it isp s l p y eI about uniform suspension of the pulp fibers in the inventiveDrinclples hereof in making P pe Prod-- 40 water and uniform dispersionof the gum particles n s of Wi y Varying is Wei ht and compact- 4gthroughout the suspension, assuming that the n n pt for m ny usesbesides that of powdered gum is added to the stock while in the taking9' Water While resisting t t onbeater-engine rather than at a laterstage of instance-n Wet-strengthened, absorptive D paper making, say,whileit is flowing as a stream per product hereof containing locust beangum as 145 to the papermaking machine, the wet-strengthening agent mayundergo a sec- 5 Typical procedures carried out accordant with ondsryimpregnation with water-repellent matethe present invention involved theuse of a mixrials of oleagin us. resinous. y tureture of equal parts byweight of bleached sulphite Thus, t ay he mp egnated with parafllp waxor and bleached kraft wood pulps. After the mixed e like to produce aepe lent paper sheet pulps were suspended in water with very littlsuitable for use as a lettuce crate-liner, for wrap- 5 hydration thereofto produce a uniform pulp sus- P E- l In such a e spheres of use. ipension of appropriate consistency for paper mak-' is d r e that theWater coming from? the ing, namely, of about 1% fiber content, locustmelted iceinwhich the heads-of lettuce or bundles bean gum was added asa'flne powder to the sus-' of celery are p k d e ep ll d bythepaper-liner .55 pension in amount to yield a paper sheet contain-Wrap ra n: gum, based on the dry weight of the pulp. So far as concernsthe alkalinization of a pre- Specifically, the powdered gum wasdispersed unir e p per W b n i ing the locust bean gum. formly in thedilute pulp suspension at the head it is possible, as already indicated,to use any box of the paper-making machine. The sheet proalkalinesolution capable of imparting to the pa- .60. duced on the papermakingmachine, which had a per a pH value greater than 1. It is thus seen onbasis weight of about 22 pounds, was pressed and that alkaline slutions, of wid ly v rying alkalindried in the. usual way on thepapermaking lty or s e are use ul for the purposes hereof machine. Thedried papersheet containing locust aiforded with alkalis or alkalinecompounds-of 85 bean gum, based on the dry weight of fiber, was manydifferent kinds, 'even though for somepur- .05 dipped into an aqueousborax solution of 1% poses, such as toweling, it is preferable t t um-lthe dried, weakly alkalinized product had a wetprovided by such mildlyalkaline con; unds a I tensile-strength of 1.4 pounds. When a solutionborax. The amount of alkaline solution used to 1 71! of 1% strength wasprayed onto a similar preactivatethe gum in situ in the gum-containing7o dried, gum-containing paper sheet in an amount paper'web is 3180'subject to wide variation, but of 300%, based on the weight -of thedried sum, it is ener lly Preferable to apply no more alka and thesprayed sheet redrled, it was found that line solution to the web thanis necessary to wet the drIedQWeakIy kalinized product'had a wetoralkalinize the web substantially uniformly g; tensile-strength of 1.8poun Sincejit appeared throughout while avoiding dripping or drainagealkalinizationor treatment with alkaline solu-' tion is dried or redriedat elevated temperature, as on the steam-heated drier drums of apapermaking machine. It is thus seen that the process hereof can bepracticed while a sheet of paper is being made at the customary highpapermaking speeds and the resulting continuous sheet of papercontaining the gum can be activated or brought to the desired highwet-strength by a1- kalinization while such sheet is pursuing its highspeed continuous course from the station of alkalinization, through thedrier, and thence to the reel.

I claim:

l. A method of making a paper product of high wet-strength, whichcomprises forming paper from paper-making stock containing powderedlocust bean gum in an amount not more than about based'on the dry weightof the stock; and alkalinizing the resulting paper with an aqueoussolution of an alkaline compound.

2. A method of making a paper product 01' high.

wet-strength, which comprises forming paper from paper-making stockcontaining powdered locust bean gum substantially uniformly dispersedtherethrough in. an amount not more than about 5%, based on the dryweight of the stock, wetting the resulting paper with an alkalinesoelevated temperature.

lution of suflicient alkalinity to impart thereto a pH value greaterthan '7, and drying the alkalinized' paper.

3. A method of making an absorptive paper product of high wet-strength,which comprises incorporating into .substantially unhydrated'papermaking stock not more than about 5% of powdered locust bean gum,based on the dry weight of the stock, forming paper from the resultingstock, alkalinizing the paper substantially uniformly with an aqueoussolution of a mildly alkaline compound, and drying the paper.

4.. A method of making an absorptive paper product of high wet-strength,which comprises incorporating into substantially unhydrated papermakingstock about 4% to 1% of powdered locust bean gum, based on the dryweight 01 the stock, forming paper from the resulting stock, wetting thepaper substantially uniformly with a solution of borax, and drying thpaper.

5; A method of making a paper roduct of high wet-strength, whichcomprises incorporating-into papermaking stock powdered locust bean gumin an amount not more than about 5%, based on the dry weight of thestock, forming paper from the resulting stock, spraying the paper with asolution of mildly alkaline compound in amount to wet the papersubstantially uniformly throughout while substantially avoiding theextraction of the gum therefrom, and drying the paper at MILTON- o.

